The word for base-64?

Although it's more of a camp or a shelter than a headquarters, you could use bivouac.

bivouac (n) - A temporary camp without tents or cover, used especially by soldiers or mountaineers.

The smaller currency unit or value, in countries that have one, is generically called a fractional monetary unit:

a monetary unit that is valued at a fraction (usually one hundredth) of the basic monetary unit

The link from Free Dictionary gives both the definition and several examples (like cent, centavo, fil, piaster). The definition also suggests that the basic unit is called just that, the basic monetary unit.

In your example, I would write:

This number describes a fractional (monetary) unit, but it needs to be converted to the basic (monetary) unit.

If you've already established you are talking about money, you can drop the "monetary," otherwise leave it as is.